Three-phase separator

ABSTRACT

A three-phase separator ( 1 ) comprising a normally horizontal vessel ( 3 ) defining a liquid separation space ( 5 ) and a gas space ( 7 ), which vessel ( 3 ) has an inlet end space ( 1 ) provided with a feed inlet ( 21 ) and an outlet end space ( 15 ) provided with separate outlets ( 25, 26  and  27 ) for the three phases, which vessel ( 3 ) further comprises an inlet device ( 31 ) comprising a primary separator ( 35 ) arranged in the gas space ( 7 ) and a tilted return tray ( 38 ) arranged in the gas space ( 7 ) having a lower end ( 39 ) that is located near the inlet end wall ( 13 ) such that a passage ( 41 ) is defined between the lower end ( 39 ) and the inlet end wall ( 13 ).

BACKGROUND OF THE INVENTION

The present invention relates to a three-phase separator, wherein a feedcomprising a gas phase and a lighter liquid and a heavier liquid phaseis separated into the three phases gas, lighter liquid and heavierliquid. Such a separator is also called a gas/liquid/liquid separator.Three-phase separators are used in the oil industry to separate amixture of hydrocarbons—gas and oil, and water into the constituentsgas, oil and water.

Examples of such separators are described in U.S. Pat. No. 3,469,373 andin the book ‘Surface Production Operations, Design of Oil-HandlingSystems and Facilities’, volume 1, 2nd edition, K Arnold and M Stewart,Gulf Publishing Company, 1998 on page 135 and further.

A known three-phase separator comprises a normally horizontal vesseldefining a liquid separation space and a gas space above the liquidseparation space, which vessel has an inlet end space provided with afeed inlet and an outlet end space provided with separate outlets forthe three phases, which vessel further comprises an inlet device in theform of an inlet diverter.

During normal operation a feed comprising a mixture of gas and liquidsis introduced through the inlet into the vessel. The feed collides withthe inlet diverter, and the sudden change of momentum causes a firstseparation of gas and liquids. Gas enters the gas space, and the liquidsenter the liquid separation space where they are separated in a lighterliquid phase and a heavier liquid phase under the influence of gravity.Gas and the liquid phases are separately removed from the vessel throughthe outlets. The inlet diverter of the known three-phase separator is avertical plate that extends into the liquid separation zone. In thisway, the diverter forces the liquids to enter the liquid-filled liquidseparation space.

A disadvantage of the known separator is a low separation capacity.

It is an object of the present invention to overcome this drawback.

SUMMARY OF THE INVENTION

To this end the three-phase separator according to the present inventioncomprises a normally horizontal vessel defining a liquid separationspace and a gas space above the liquid separation space, which vesselhas an inlet end space provided with a feed inlet and an outlet endspace provided with separate outlets for the three phases, which vesselfurther comprises an inlet device comprising a primary separator whichis arranged in the gas space and a tilted return tray arranged in thegas space under the primary separator having a lower end that is locatednear the inlet end wall of the vessel, such that a passage is definedbetween the lower end and the inlet end wall.

Applicants found that with the separator according to the invention ahigher separation capacity can be achieved. Without wanting to belimited in any way by the following theory, applicants believe that theimproved capacity is achieved because the liquid is guided to the liquidseparation space via the inlet end wall of the separator. Because ofthis guiding of the liquid flow less turbulence in the liquid phaseresults as compared to the prior art devices. Because of the decrease inturbulence a more efficient settling of the liquid-liquid phases willresult and hence an improved separation efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example in more detailwith reference to the accompanying drawings, wherein

FIG. 1 shows schematically a longitudinal section of the three-phaseseparator according to the present invention;

FIG. 2 shows schematically a section along line II—II of the inletdevice of FIG. 1;

FIG. 3 shows schematically an alternative arrangement of the primaryseparator;

FIG. 4 shows schematically a cross-section of an alternative of thereturn tray shown in FIG. 1;

FIG. 5 shows schematically a cross-section of another alternative of thereturn tray shown in FIG. 1; and

FIG. 6 shows schematically an alternative arrangement of the liquidseparation system.

FIG. 7 shows a cross-sectional view AA′ of FIG. 8 illustratingseparating enhancing means in the liquid space.

FIG. 8 shows an elongated cross-sectional view BB′ of the vessel of FIG.7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made to FIG. 1. The three-phase separator 1 accordingto the present invention comprises a normally horizontal vessel 3. Thevessel 3 defines a liquid separation space 5 and a gas space 7 above theliquid separation space 5.

The vessel 3 has an inlet end space 11 having an inlet end wall 13 andan outlet end space 15 having an outlet end wall 17. The inlet end space11 is provided with a feed inlet 21. The outlet end space 15 is providedwith a liquid separation system in the form of a weir 22 that extendsover the width of the vessel 3. Furthermore, the outlet end space 15 isprovided with separate outlets 25, 26 and 27 for the three phases, gas,heavier liquid and lighter liquid.

The vessel 3 further comprises an inlet device 31, which inlet device 31comprises a primary separator. The primary separator may be anygas-liquid separator arranged in the gas space 7, which, in use, resultsin a downwardly discharged liquid flow in said gas space 7. Examples ofpossible separators are separators comprising a plurality of swirl tubesor a half-open pipe. A further example is a vane pack separator asdescribed in WO-A-9823351. Suitably the primary separator is a vane-typeseparator, which is arranged in the gas space. The vane-type separatoris suitably a so-called Schoepentoeter inlet device 35 as illustrated inFIG. 1. A preferred Schoepentoeter inlet device is exemplified inGB-A-1119699. The preferred Schoepentoeter inlet device 35 comprises aninlet 36 that is in fluid communication with the feed inlet 21. Inlet 36comprises a number of evenly spaced vertical vanes 37 placed one behindthe other between a top plate 36″ and a bottom plate 36′. Each vane 37comprises an outwardly directed deflecting part.

During normal operation a mixture of gas and liquids is supplied to thefeed inlet 21. This mixture then flows through the inlet 36 of theSchoepentoeter device 35. The vanes 37, arranged on either side of aflow path in the inlet 36, deflect the mixture outwardly. The change inthe direction of flow causes a gas-liquid separation.

The inlet device 31 further comprises a tilted return tray in the formof a tilted guide plate 38, which is arranged in the gas space 7 underthe primary separator 35. The tilted guide plate 38 has a lower end 39that is located near the inlet end wall 13 of the vessel 3 such that apassage 41 is defined between the lower end 39 and the inlet end wall13. The size of the tilted guide plate 38 is at least equal to the sizeof the primary separator.

During normal operation, a feed comprising a mixture of gas and liquidsis introduced through the inlet 21 into the vessel 3. A first separationis done in the vane-type separator 35: gas enters the gas space 7 fromwhich it is removed through outlet 25, and liquid emerges from thevane-type separator 35 in the direction of the vanes 37 and descends.

The liquid falls on the tilted return tray in the form of guide plate 38and is guided by the tilted guide plate 38 towards the passage 41.Through that passage the liquid enters the liquid separation space 5. Inthe liquid separation space 5, the liquid is separated into a lighterliquid phase 43 and a heavier liquid phase 44 under the influence ofgravity. The heavier liquid phase 44 settles in the lower part of theliquid separation space 5 and the lighter liquid phase 43 floats on topof the heavier liquid phase 44. The interface between the phases isdesignated with reference numeral 45.

The outlet end space 15 is provided with the liquid separation system inthe form of the weir 22. The lighter liquid flows over the weir 22 to acollecting space 46, from which it is removed through outlet 27. Theheavier liquid is removed from the liquid separation space 5 throughoutlet 26. In this way gas and liquid phases are separately removed fromthe vessel 3.

In the absence of the tilted guide plate 38, the separated liquid wouldplunge into the liquid separation space 5, where it would generateturbulence so that mixing between the liquid phases will take place.Such mixing adversely affects the separation performance of thethree-phase separator. Moreover the liquid is discharged over the lengthof the primary separator 35. This leads to a loss of effectiveseparation space. Also gas is entrained in the liquid space.Furthermore, in the gas space vortices are formed, because gas flowingout of the primary separator, and especially out of the vane-typeseparators 35, is directed downwards by the wall of the vessel 3. Thesevortices generate vortices in the liquids present in the liquidseparation space 5, which causes additional mixing that has an adverseeffect on the separation efficiency. The tilted return tray 38, however,reduces both gas-liquid and liquid-liquid mixing because it forms aseparation between the gas space 7 and the liquid separation space 5.Furthermore the tilted return tray enlarges the liquid separation space5, because the liquids are introduced in it through the passage 41 nearthe inlet end wall 13. The enlarged separation space 5 improves theseparation capacity for a given size of the vessel 3.

Reference is now made to FIG. 3 showing schematically a part of alongitudinal section of the three-phase separator of the presentinvention with an alternative arrangement of the primary separator. InFIG. 3, the elements have been referred to with the reference numeralsused in FIGS. 1 and 2. In this embodiment, the primary separator 35 isso directed that, during normal operation, the direction of fluid flowthrough the primary separator 35 is the same as the direction of thefluids flowing over the tilted guide plate 38.

The three-phase separator may further include a vertical liquiddistributor plate 49 (see FIG. 3) arranged in the liquid separationspace 5. Such a distribution plate is a plate provided with openings.Because of such a plate a more even distribution of the liquid flow inthe liquid space downstream the distributor is achieved. The net freearea of such a plate is preferably between 10 and 30%. The diameter ofthe openings is preferably between 0.005 and 0.025 m.

The tilted return tray should be so designed that it captures at leastthe majority of the liquid emerging from the primary separator. Toachieve this, the return tray can be the tilted guide plate 38, whichsuitably extends over the width of the vessel 3. This embodiment isparticularly suitable when the liquid emerging from the primaryseparator is evenly distributed over the width of the vessel.

Alternatives of the tilted guide plate are shown schematically in FIGS.4 and 5. FIG. 4 shows a tilted return tray in the form of a plurality ofoverlapping troughs 50 arranged in a zigzag order. FIG. 5 shows a tiltedreturn tray in the form of a plurality of adjacent troughs 51 andinclined guide plates 52, which direct the liquid to the troughs 51. Anadvantage of the return trays shown in FIGS. 4 and 5 is that they areopen to gas flow so that they do not hamper axial gas flow. The troughs50 and 51 and the inclined guide plates 52 are tilted in a directionperpendicular to the plane of drawing.

Reference is now made to FIG. 2. Liquid will emerge from the primaryseparator towards the side of the vessel, and thus the section of thereturn tray under the primary separator receives hardly any liquid. Thusa return tray that is open to gas flow can as well be obtained by makinga longitudinal slit in the return tray under the primary separator. Thereturn tray then comprises two tilted plates arranged at either side ofthe vessel.

The length of the tilted return tray is suitably equal to the length ofthe primary separator. The angle of tilt of the tilted return tray issuitable between 5° and 15°.

In the embodiment as discussed with reference to FIG. 1, the liquidseparation system is a weir 22 that extends over the width of the vessel3. However, there are several alternative liquid separation systemspossible, for example, the weir 22 can be replaced by a cylinder of thesame height that is placed over the outlet 27 for the lighter liquidphase.

Another alternative is shown in FIG. 6 showing schematically a part of alongitudinal section of the three-phase separator of the presentinvention with an alternative arrangement of the liquid separationsystem. In this embodiment the liquid separation system comprises atrough 53 and a weir 54, wherein both the trough 53 and the weir 54extend over the width of the vessel 3. The walls of the trough 53 arehigher than the weir 54 so that during normal operation the lighterliquid phase 43 flows into the trough 53, and the heavier liquid flowsover the weir 54 into a collecting space 55. The lighter liquid iswithdrawn via outlet conduit 56 and the heavier liquid is withdrawn viaoutlet conduit 57.

Preferably the liquid space is provided with means to enhance theseparation of the liquid phases in the liquid space. Because lessdisturbance in the liquid space near the inlet end wall is achieved, asexplained above, a greater part of the liquid space may be provided withthese means to enhance the separation. A preferred separation means isillustrated in FIGS. 7 and 8.

FIG. 7 illustrates a cross-sectional view AA′ of the vessel shown inFIG. 8, which vessel is further provided with separation enhancing means58. The separating enhancing means 58 comprise at least two stacks 59 ofsloping vertically spaced plates 60 and so disposed that on one side ofeach stack there exists a vertical collecting channel 61 towards whichthe plates of the stack slope downwardly, and at the opposite side ofthe same stack there exists a vertical collecting channel 62 towardswhich both plates of the stack slope upwardly. The space above thestacks provides a collecting chamber 63 for the lighter liquid phase 43and the space below the stacks provides a collecting chamber 64 for theheavier liquid phase 44. Via vertical collecting channel 62 lighterliquid phase 43 will move upwardly and through vertical collectingchannel 61 heavier liquid phase 44 will move downwardly duringliquid-liquid separation. Such a separation enhancing means is furtherexemplified in U.S. Pat. No. 3,563,389.

FIG. 8 shows an elongated cross-sectional view BB′ of the vessel of FIG.7. FIG. 8 also shows a gas distributor plate 65, a liquid distributorplate 49 and a slug tray 66. FIG. 8 shows a preferred embodiment whereina second tilted return tray 67 is present below vane-type separator 35,arranged parallel to the first tray 38 and such that a second passage isdefined at its lower end between the lower end of the first tilted trayand the top end of the liquid distributor plate 49. The gas distributorplate 65 divides a gas space near the inlet end wall and the remainingpart of the gas space. The gas distributing plate 65 is suitably a plateprovided with openings. The gas distributing plate 65 enhances a moreevenly distributed gas flow downstream of the plate 65. The plate 65further forms a wave breaker when, due to slugging flow a large amountof liquid suddenly enters the three-phase separator 1. Preferably thedistance between the inlet device 31 and the gas distributing plate 65is between 1 and 3 times the diameter of the feed inlet 21. The net freearea of such a plate 65 is preferably between 10 and 30%. The diameterof the openings is preferably between 0.005 and 0.025 m.

The three-phase separator is preferably further provided with a slugtray 66 between the tilted return tray 38 or second tilted tray 67, ifpresent, and the gas distributing plate 65. The slug tray 66 is slopedsuch that the lower end is located near the gas distributing plate 65.This slug tray 66 is so positioned that, when In use, slugs are guidedto the liquid separation phase at a position far away from the inlet endwall 13. This results in less disturbance in the liquid phase near theinlet end wall 13. The upper end of the slug tray 66 preferablyterminates at the upper end of the tilted guide plate 38 or secondtilted tray 67, if present. The lower end of the slug tray 66 preferablyterminates just below the normal liquid level of the liquid presentliquid separation space 7 and near gas distributing plate 65.

Because liquid distributing plate 49 can be placed nearer to the inletend wall 13 more space is provided for the separation enhancing means 58as shown in FIG. 8. The stacks 59 extend preferably from liquiddistributor 49 to the liquid separation system, i.e. weir 22. Becausemore length of the vessel can be used for liquid-liquid separation afurther increase of separation capacity results.

What is claimed is:
 1. A three-phase separator comprising a normallyhorizontal vessel defining a liquid separation space and a gas spaceabove the liquid separation space, which vessel has an inlet end spaceprovided with a feed inlet and an outlet end space provided withseparate outlets for the three phases, which vessel further comprises aninlet device comprising a primary gas-liquid separator which is arrangedin the gas space and a tilted return tray arranged in the gas spaceunder the primary separator having a lower end that is located near theinlet end wall of the vessel, such that a passage is defined between thelower end and the inlet end wall.
 2. Three-phase separator according toclaim 1, wherein the tilted return tray extends over the width of thevessel.
 3. Three-phase separator according to claim 1, wherein thetilted return tray comprises a plurality of overlapping troughs arrangedin a zigzag order.
 4. Three-phase separator according to claim 1,wherein the tilted return tray comprises a plurality of adjacent troughsand inclined guide plates, which direct during normal operation theliquid to the troughs.
 5. Three-phase separator according to claim 1,wherein the tilted return tray comprises two tilted plates arranged ateither side of the vessel.
 6. Three-phase separator according to claim1, wherein the length of the tilted return tray is equal to the lengthof the primary separator.
 7. Three-phase separator according to claim 1,wherein the angle of tilt of the tilted return tray is between 5° and15°.
 8. Three-phase separator according to claim 1, wherein the primaryseparator comprises an inlet fluidly communicating with a feed inlet,which inlet comprises a number of evenly spaced vertical vanes placedone behind the other between a top plate and a bottom plate, which vanescomprise an outwardly directed deflecting part.
 9. Three-phase separatoraccording to claim 1, wherein a plate with openings is present in thegas space dividing a gas space near the inlet end wall and the remainingpart of the gas space.
 10. Three-phase separator according to claim 9,wherein the distance between the inlet device and the plate withopenings is between about 1 and 3 times the diameter of the feed inletwhich is fluidly connected to the primary separator.
 11. Three-phaseseparator according to claim 10, wherein a slug tray is present in thegas space near the inlet end wall and between the tilted return tray andthe plate with openings and wherein the slug tray is sloped such thatthe lower end is located at the plate with openings.
 12. Three-phaseseparator according to claim 11, wherein in the liquid separation spacebelow the tilted return tray a vertical distribution plate is presentdividing a liquid space near the inlet end wall and the remaining partof the liquid separation space.
 13. Three-phase separator according toclaim 12, wherein the remaining part of the liquid separation space isprovided with at least two stacks of sloping vertically spaced platesand so disposed that on one side of each stack there exists a verticalcollecting channel towards which the plates of the stack slopedownwardly, and at the opposite side of the same stack there exists avertical collecting channel towards which both plates of the stack slopeupwardly.
 14. Use of a three-phase separator comprising a normallyhorizontal vessel defining a liquid separation space and a gas spaceabove the liquid separation space, which vessel has an inlet end spaceprovided with a feed inlet and an outlet end space provided withseparate outlets for the three phases, which vessel further comprises aninlet device comprising a primary gas-liquid separator which is arrangedin the gas space and a tilted return tray arranged in the gas spaceunder the primary separator having a lower end that is located near theinlet end wall of the vessel, such that a passage is defined between thelower end and the inlet end wall to separate a mixture of gas, oil andwater into the constituents gas, oil and water.